The prospect of infections spreading from animals to humans has become all too real with the onset of the current swine flu pandemic, and the threat of a bird flu still looming. But infections can jump the other way too. Decades before the world's media were gripped with panic over bird flu, humans transferred a disease to chickens and it has since caused a poultry pandemic right under our noses.
The infection in question is a familiar one - Staphylococcus aureus, a common human bacterium that's behind everything from mild skin infections to life-threatening MRSA. It causes chicken diseases too, including septic arthritis and 'bumblefoot'. But in the 1970s, broiler chickens began developing a new type of S.aureus infection called 'bacterial chrondronecrosis with osteomyelitis' or, more simply, BCO. It's a bone infection and it's a major cause of lameness in broiler chickens.
This new disease had human origins. Bethan Lowder from the University of Edinburgh has shown that all of the bacteria behind BCO share a common ancestor, which jumped from humans to chickens in Poland, around 38 years ago. From that point on, the bacterium's travel itinerary was set. Just as air travel has facilitated the spread of swine flu among humans, a global distribution network for chickens made it easy for S.aureus to spread all over the world aboard its new feathery hosts.
